+ // Calculate the repetition info. It is the ply distance from the previous
+ // occurrence of the same position, negative in the 3-fold case, or zero
+ // if the position was not repeated.
+ st->repetition = 0;
+ int end = std::min(st->rule50, st->pliesFromNull);
+ if (end >= 4)
+ {
+ StateInfo* stp = st->previous->previous;
+ for (int i=4; i <= end; i += 2)
+ {
+ stp = stp->previous->previous;
+ if (stp->key == st->key)
+ {
+ st->repetition = stp->repetition ? -i : i;
+ break;
+ }
+ }
+ }
+